I plan to use it so I can automatically pull up the last opened panel in LibAddonsMenu after a reloadui was issued to apply some settings that cannot be set without one.
I guess I could make it work with some callLater magic, but I think it would be more straight forward if I get the event on UI reload instead of game start. Maybe you can add 2 different events for both cases? I can think of at least one other feature I want to implement that would need the event on first load.
EDIT: Or maybe you could change EVENT_PLAYER_ACTIVATED so it passes a parameter which can be used to identify the reason for the event (game start, ui reload, zone change, etc).